Implement NOWAIT option for BASE_BACKUP command

Specifying this option makes the server not wait for the
xlog to be archived, or emit a warning that it can't,
instead leaving the responsibility with the client.

This is useful when the log is being streamed using
the streaming protocol in parallel with the backup,
without having log archiving enabled.

src/backend/replication/basebackup.c

@@ -37,6 +37,7 @@ typedef struct
 	const char *label;
 	bool		progress;
 	bool		fastcheckpoint;
+	bool		nowait;
 	bool		includewal;
 }	basebackup_options;
 
@@ -173,7 +174,7 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 	}
 	PG_END_ENSURE_ERROR_CLEANUP(base_backup_cleanup, (Datum) 0);
 
-	endptr = do_pg_stop_backup(labelfile);
+	endptr = do_pg_stop_backup(labelfile, !opt->nowait);
 
 	if (opt->includewal)
 	{
@@ -260,6 +261,7 @@ parse_basebackup_options(List *options, basebackup_options *opt)
 	bool		o_label = false;
 	bool		o_progress = false;
 	bool		o_fast = false;
+	bool		o_nowait = false;
 	bool		o_wal = false;
 
 	MemSet(opt, 0, sizeof(*opt));
@@ -294,6 +296,15 @@ parse_basebackup_options(List *options, basebackup_options *opt)
 			opt->fastcheckpoint = true;
 			o_fast = true;
 		}
+		else if (strcmp(defel->defname, "nowait") == 0)
+		{
+			if (o_nowait)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("duplicate option \"%s\"", defel->defname)));
+			opt->nowait = true;
+			o_nowait = true;
+		}
 		else if (strcmp(defel->defname, "wal") == 0)
 		{
 			if (o_wal)

src/backend/replication/repl_gram.y

@@ -71,6 +71,7 @@ Node *replication_parse_result;
 %token K_LABEL
 %token K_PROGRESS
 %token K_FAST
+%token K_NOWAIT
 %token K_WAL
 %token K_START_REPLICATION
 
@@ -107,7 +108,7 @@ identify_system:
 			;
 
 /*
- * BASE_BACKUP [LABEL '<label>'] [PROGRESS] [FAST] [WAL]
+ * BASE_BACKUP [LABEL '<label>'] [PROGRESS] [FAST] [WAL] [NOWAIT]
  */
 base_backup:
 			K_BASE_BACKUP base_backup_opt_list
@@ -142,6 +143,11 @@ base_backup_opt:
 				  $$ = makeDefElem("wal",
 						   (Node *)makeInteger(TRUE));
 				}
+			| K_NOWAIT
+				{
+				  $$ = makeDefElem("nowait",
+						   (Node *)makeInteger(TRUE));
+				}
 			;
 
 /*

src/backend/replication/repl_scanner.l

@@ -60,6 +60,7 @@ BASE_BACKUP			{ return K_BASE_BACKUP; }
 FAST			{ return K_FAST; }
 IDENTIFY_SYSTEM		{ return K_IDENTIFY_SYSTEM; }
 LABEL			{ return K_LABEL; }
+NOWAIT			{ return K_NOWAIT; }
 PROGRESS			{ return K_PROGRESS; }
 WAL			{ return K_WAL; }
 START_REPLICATION	{ return K_START_REPLICATION; }